Alate and apterous virginoparae ofAphis fabae Scop, and alate virginoparae ofBrevicoryne brassicae (L.), walking in a linear track olfactometer, were attracted by odor from leaves of their host plants.A. fabae responded to odor from undamaged but not damaged bean leaves. Gynoparae (autumn migrants) ofA. fabae, however, did not respond to their host plant (spindle,Euonymus europaeus) odor. Odors of certain nonhost plants masked the attractiveness of the host plant leaves, but tansy (Tanacetum vulgare) and summer savory (Satureja hortensis) volatiles repelledB. brassicae andA. fabae, respectively. 3-Butenyl isothiocyanate attractedB. brassicae andLipaphis erysimi (Kalt.), the latter species being more sensitive in both behavioral and electrophysiological studies. Isothiocyanate receptors were found on the antennae ofA. fabae, which was repelled by these compounds, 4-pentenyl isothiocyanate being the most active.

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SummarySex pheromone released by Megoura viciae oviparae was collected and analysed for the quantity and relative amounts of each of the two biologically active components. Pheromone was not produced until the second day of the adult stadium, increäsing in quantity up to day 6 and then declining. The ratio of (-)-(1R, 4aS, 7S, 7aR)-nepetalactol: (+)-(4aS,7S,7aR)-nepetalactone pheromone mixture changed from ca 1:5 on days 2-6 after adult moult to 1:12 on days 7 and 8, but returned to the original composition by day 10.The behaviour of male aphids from three species, Aeyrthosiphon pisum, Aphis fabae, and M. viciae, was observed in an olfactometer and in two mating bioassays, using both synthetic and natural sex pheromone. The two active components were combined in ratios which mimicked the pheromone released by these and other aphid species. It was found that:1. M. viciae males were attracted by the synthetic sex pheromone in the olfactometer, with maximal attraction to the conspecific ratio. On the other hand, A. pisum and A. fabae males did not respond to any pheromone mixtures in the olfactometer. 2. Males of all three species could be induced to attempt copulation with conspecific virginoparae treated with synthetic pheromone (virginoparae reproduce asexually and do not produce the sex pheromone). The response in M. viciae and A. fabae was equivalent to that elicited by natural pheromone released by calling conspecific oviparae, but in A. pisum it was slightly lower. 3. In M. viciae, the relative activities of the nepetalactol and the nepetalactone were reversed in the two assays. Thus the former was more potent in the mating bioassay, the latter in the olfactometer. The nepetalactol appeared to act as an aphrodisiac and the nepetalactone as an attractänt. 4. Mating response was greatest at the species-specific ratio of the two components, but males were also significantly responsive to mixtures mimicking the sex pheromone of other species.The results are discussed in relation to mate seeking, together with the mechanisms involved in speciesspecific mating. Key wordsconspecific mating, attraction, sex pheromone, olfactometer, nepetalactol, nepetalactone, Homoptera, Aphidae, Acyrthosiphon pisurn, Aphis fabae, Megoura viciae lntroduction Pettersson (1970aPettersson ( , 1971 and Marsh (1972) first observed that sexual female aphids (oviparae) released a sex pheromone which attracted males. The pheromone was released from scent plaques on the hind tibiae and detected by olfactory sensilla on male antennae. They also reported that

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Abstract. Walking alate virginoparae of Brevicoryne brassicae (L.) and Aphis fabae Scopoli were presented with odours of steam‐distilled extracts of the non‐host plants summer savoury (Satureja hortensis L.) and tansy (Tanacetum vulgare L.) in an olfactometer. No effects of the extracts were observed on B. brassicae. However, A.fabae were repelled by summer savoury and tansy odour; both extracts also masked an attractant response to bean (host plant) odour. In a flight chamber, air permeated with odour from host or non‐host plants was blown over flying alates of both species, with a green, plant‐mimicking target presented once a minute. The incidence of targeted (host‐responsive) flight of B.brassicae was not affected by odour from a growing host plant (Brassica oleoracea) or a non‐host plant tansy. Host plant (Vicia faba) odour did not affect the initial rate of climb or the incidence of targeted flight of A.fabae, but when the bean odour was alternated with odour from non‐host tansy plants a greater number of targeted flights occurred in the host plant odour. The volatile extracts of tansy and summer savoury were also presented to flying A.fabae. Aphids flying in air permeated with tansy odour at 450g plant equivalents initiated fewer targeted flights than when flying in clean air. However, no differences in flight behaviour were observed with summer savoury extract. In a horizontal wind tunnel the tansy extract at 90 g plant equivalents blown across the surface of yellow targets reduced the numbers of alate A.fabae landing. The results indicate that plant odours can affect flight and landing of aphids.